This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
Nor has Nature, in the case of the Dog, merely given to man a servant endowed with sagacity and zeal: man has need of help in various ways, and under very different circumstances. In bodily strength he is unable to cope with ferocious enemies that surround him on all sides; his senses are imperfect, when compared with those of some of the lower animals; in speed he is outstripped by the very creatures appointed to be his food: how then are all these deficiencies to be compensated? The Dog has been placed at man's disposal: its instincts, its size, its form, its senses, and its corporeal attributes are all subjugated to his control; and thus whatever aid he may require is to be obtained by the cultivation of its faculties.
(2226). The Plantigrade Carnivora, as their name indicates, in walking apply the entire sole of the foot to the ground, as far back as the end of the os calcis: such are the Bear (Ursus), the Glutton (Gulo), the Badger (Meles), and others of similar organization. These tribes are less exclusively carnivorous in their habits than the preceding; and their nails are not retractile, so that their points are blunted by dragging upon the ground.
(2227). The Insectivora form another section of these destructive quadrupeds, distinguished by their molar teeth being studded with sharp points, and thus calculated to devour insect prey: the Hedgehog (Erinaceus), the Shrew (Sorex), and the Mole (Taipa) are well-known examples of this division, and their habits are known to all. We need scarcely mention the peculiar circumstances under which the Mole passes its subterranean existence, or the extraordinary conformation of its anterior extremities, whereby they are converted into most efficient instruments for digging beneath the soil. The extended scapula, the strong and well-developed clavicle, the square and massive humerus, and, moreover, the broad and rake-like hand, all proclaim the office of this strange limb; while the long and carinated sternum indicates with equal plainness the size and power of those muscles by which the apparatus is wielded *.
(2228). The Cheiroptera, or family of Bats, present a striking contrast to the Mole both in form and habits: neither would it be easy to conceive that a skeleton, consisting almost of precisely the same elements, could be converted to uses so diametrically opposite.
(2229). In these Mammalia the anterior extremities are converted into wings, enabling them to emulate the very birds in their powers of flight, and in the velocity of their movements when upon the wing pursuing insect prey. In creatures destined to such a life, the whole skeleton must of course be lightened, and the bones attenuated to the utmost. The skull, the spine, the thorax, the pelvis, and the hind extremities, all testify, by the delicacy of their structure, that no unnecessary weight is here permitted. It is, however, in the construction of the anterior limbs that the Cheiroptera present the most remarkable peculiarities. The scapulae are broad and expanded, covering a considerable portion of the back of the thorax, thus giving a firm basis to the wing. The clavicles are large and perfectly formed, in order to resist the powerful action of the pectoral muscles used in depressing the wings during flight; and in order to give those muscles a sufficient extent of origin, the sternum, although exhibiting the general characters of that of a quadruped, is deeply carinated along the mesial line. The humerus is of moderate length, but the fore-arm prolonged and slender; it consists, in fact, of but one bone, so that all movements of pronation and supination are necessarily impracticable.
The carpal bones present their usual structure and arrangement at the base of the hand; but those of the metacarpus, excepting that of the thumb, are so extraordinarily lengthened, that they themselves form a considerable portion of the framework of the wing, which is completed by the phalanges of the fingers appended to their extremities. All these wirelike fingers are connected together by a broad duplicature of skin, derived from the sides of the body, which is continued along the whole length of the hind legs, and even fills up the interspace between these last and the tail: this membrane forms an expansion sufficiently extensive to become converted into an organ of flight. The fingers composing this strange hand are obviously incapable of closing towards the palm, as ours do when grasping an object: their only movements are such as fold up the wing against the side of the body, by laying the fingers close along the side of the fore-arm, as in closing a fan. The thumb alone is left free; and this being short, and armed with a strong nail, is employed in enabling the creature to cling to some elevated object in those gloomy lurking-places wherein it hides during the day. (2230.) The Quadrumana, next to mankind the most elevated members of the animal creation, are, as is evident from every point of their organization, the destined inhabitants of the trees; neither will it appear astonishing, when we consider the extensive provision that has been made for the support of animal life amid the dense and pathless forests of tropical climates, that animals so intelligent, and capable of enjoyment, should have been widely disseminated through extensive regions of our globe.
* For an admirable history of the habits of the Mole, the reader is referred to Bell's British Quadrupeds, page 85.
Fig. 394. Skeleton of the Bat.
(2231). The great distinction characteristic of the Quadrumana is found in the organization of their feet, all of which are converted into prehensile instruments, whereby they can seize the boughs of the trees wherein they reside, and thus securely swing themselves from branch to branch, or even leap from one tree to another, with wonderful activity and precision. Their hands are constructed upon the same principle as those of Man, - their thumbs, although less perfectly formed than our own, being opposable to the other fingers, and thus securing a firm and steady grasp. The bones of the fore-arm are free, and accurately articulated with each other; the pronation and supination of the hand are, therefore, accomplished with facility. In the construction of the feet the same provisions have been made to enable them to take a firm grasp: the toes, like the fingers of the hand, are long and flexible, and the representative of the great toe is converted into a very perfect thumb, easily opposable to the rest; the foot, or posterior hand, therefore, equals, or even surpasses, in its powers of prehension, the hand which terminates the anterior limb.